ReviewThe role of manufacturers in reducing biofilms in dental chair waterlines
Introduction
Modern dental chair units (DCUs) are classified as medical devices under the EU Medical Devices Directive.1 According to this Directive, a medical device is “any instrument, apparatus, appliance, material or other article, whether used alone or in combination, including the software necessary for its proper application, intended by the manufacturer to be used for human beings for the purpose of diagnosis, prevention, monitoring, treatment or alleviation of disease”. Microbial contamination of a wide range of medical devices, such as anaesthetic equipment, laryngoscopes, endoscopes, gastroscopes, mechanical ventilators, resuscitation tubes, colonoscopes and catheters, has been recognised as an important cause of cross-contamination and cross-infection, especially in the hospital setting.2 Wet or moist sites or surfaces of medical devices have been particularly associated with cross-infection and cross-contamination because such areas are conducive to the growth of microbial biofilm. Because DCUs are used in the treatment of many patients throughout each day, microbial contamination of specific component parts is an important potential source of cross-infection.2 Of particular concern are parts of DCUs that come into direct contact with the patient's oral cavity, including dental unit handpieces, three-in-one air/water syringes and suction hoses. DCU output water is also of concern as a source of potential cross-infection as it comes directly from the DCU and enters the oral cavity of the patient during treatment.2 Furthermore, droplets and aerosols generated by DCU handpieces may be inhaled by patients and dental healthcare personnel.[3], [4], [5], [6]
DCUs consist of several complex, integrated equipment systems that are central to the practice of modern dentistry. These systems are designed to provide the instruments and services necessary for a diverse range of dental procedures.[6], [7], [8] DCUs use water to cool and irrigate a variety of DCU-supplied instruments and tooth surfaces during dental procedures, as the heat generated during instrument operation can be detrimental to teeth.[4], [9], [10] DCU-supplied water is also used for oral rinsing by patients during and following dental treatment and to wash out the DCU spittoon, or cuspidor, after oral rinsing. DCUs supply water as a coolant and irrigant to turbine and conventional handpieces, ultrasonic scalers, three-in-one air/water syringes, as well as providing water for the patient rinse cup filler and cuspidor via an intricate network of interconnected narrow-bore tubes called dental unit waterlines (DUWs).[7], [8]
Over the last 20 years many studies have shown that water from DUWs is often contaminated with high densities of microorganisms, predominantly bacterial species.[7], [8], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23] This is a universal problem and all untreated DUWs in standard DCUs are subject to contamination and will host resident biofilms. Microbial contamination of DUWs originates predominantly in the DCU water supply, which usually contains low levels of microorganisms.[15], [22] In a typical modern DCU the waterline distribution network consists of several meters of plastic DUW tubing with an internal diameter of a few millimeters in which water can stagnate when the equipment is not being used.[16], [18] Microorganisms in water supplied to DCUs, predominantly aerobic heterotrophic Gram-negative environmental bacteria, attach to the internal surfaces of the DUW tubing and form microcolonies that eventually give rise to multispecies biofilm.[17], [20], [22] DUW biofilms are composed mainly of highly hydrated bacterial exopolysaccharide secreted by bacteria that contain microcolonies and single cells interspersed heterogeneously with channels or pores.[23], [24] Biofilm primarily forms in DUWs because water at the internal surface of the narrow-bore waterline tubing flows more slowly than water at the centre and thus there is little disturbance to any microorganisms present.16 This permits the microorganisms to multiply and subsequently disperse through the water supply as planktonic forms where they may be deposited at other sites within the waterline network or are transferred directly into the mouths of patients during dental procedures. For these reasons DUW biofilm acts as a reservoir for continuing contamination of DCU output water. Fig. 1, panels (a) and (b) show examples of biofilm in DUWs. Sterilisation of the handpieces, syringes and associated instruments makes no impact on biofilm within DUWs whatsoever.
The occurrence of high densities of microorganisms in DCU output water (up to 106 cfu/mL has been reported) constitutes a potential risk of infection for dental patients and dental healthcare and support staff and is diametrically opposed to good infection control practices.[14], [22], [25] Furthermore, it is ethically unacceptable to knowingly expose patients, dental healthcare staff and support staff to heavily contaminated water even if the assessable cross-infection risk is considered to be low. Previous studies have shown that bacteria in DCU output water are aerosolised by DCU handpieces during dental procedures and that dental personnel and patients are exposed to these microorganisms, to fragments of DUW-derived biofilm and to waterborne bacterial endotoxin, the latter consisting of lipopolysaccharide released from the cell walls of dead Gram-negative bacteria.[13], [26], [27], [28], [29], [30] Most of the bacterial species found in DCU output water are Gram-negative aerobic heterotrophic environmental bacterial species that exhibit very low pathogenicity although they may be of concern in the treatment of vulnerable patients, such as immunocompromised and medically compromised individuals.[7], [17], [20], [22] Nonetheless there is considerable potential for infection with some bacterial pathogens found in DCU output water such as Pseudomonas aeruginosa, Legionella pneumophila and non-tuberculosis Mycobacterium species.[13], [27], [29], [31] Only a few instances of cross-infection related to DUWs and associated biofilm have been reported in the literature.[13], [29] However, it is still possible that DCU output water-associated infections have gone undetected or unreported because of the failure to associate exposure to DCU output water and aerosols generated from this water with the development of specific infections. Sporadic infections not requiring hospital admission are also less likely to be investigated.
Section snippets
Water quality standards
According to the EU Medical Devices Directive “the devices and manufacturing processes must be designed in such a way as to eliminate or reduce as far as possible the risk of infection to the patient, user and third parties”.1 Thus DCU manufacturers have an important responsibility to design for reduced risk of biofilms and also to provide detailed and specific instructions in relation to control of DUW biofilm in the DCUs they manufacture and market to dental clinics and dental practitioners.
Biofilm control in DUWs
As mentioned above, until recently, responsibility for dealing with the problem of biofilm in DUWs has been considered the duty of the dental practitioner. DCU manufacturers have been slow to respond to the obvious need for DCU engineering and design changes to control DUW biofilms. Over the last 20 years numerous proposals, both chemical based and non-chemical based, for reducing the bacterial density in DCU output water have been suggested but none has been universally adopted that is both
Conclusions
Despite the increasing complexity and sophistication of DCUs, some of the fundamental issues concerning cross-infection control and biofilm establishment in DUWs have not yet been satisfactorily resolved. These difficulties arise from a number of quarters. First, there is no universally agreed standard for the quality of output water from a DCU and, in fact, there is often no specification regarding the quality of water supplied to the DCU either. These are clearly matters for the attention of
Acknowledgements
Research and development on DUW biofilm control systems and the development of solutions to DUW disinfection failure undertaken in the authors’ laboratory was supported by the Dublin Dental Hospital Board and the Microbiology Research Unit, Dublin Dental School & Hospital. We thank Declan Clarke from the Dublin Dental Hospital Building's Department for technical assistance with the DCUs. We especially wish to thank Jari-Pekka Teravainen, Tiina Sydanlammi, Kaisu Ilomaki, Anu Matilainen and Elina
References (77)
- et al.
Bacterial aerosols in the dental clinic: a review
International Dental Journal
(2001) - et al.
The effect of handpiece spray patterns on cutting efficiency
Journal of the American Dental Association
(2002) - et al.
Aerosols and splatter in dentistry: a brief review of the literature and infection control implications
Journal of the American Dental Association
(2004) - et al.
Bacterial contamination of dental chair units in a modern dental hospital caused by leakage from suction system hoses containing extensive biofilm
The Journal of Hospital Infection
(2005) - et al.
A novel automated waterline cleaning system that facilitates effective and consistent control of microbial biofilm contamination of dental chair unit waterlines: a one-year study
Journal of Dentistry
(2006) - et al.
Optimisation of the long-term efficacy of dental chair waterline disinfection by the identification and rectification of factors associated with waterline disinfection failure
Journal of Dentistry
(2007) Pulpal response to dental techniques and materials
Dental Clinics of North America
(1971)Prevention of pulpal damage
Dental Clinics of North America
(1972)- et al.
The microbiological quality of water in dental chair units
The Journal of Hospital Infection
(1993) - et al.
Microbial contamination of dental unit waterlines: prevalence, intensity and microbiological characteristics
Journal of the American Dental Association
(1993)
Microbial contamination of dental unit waterlines: the scientific argument
International Dental Journal
The dental unit waterline controversy: defusing the myths, defining the solutions
Journal of the American Dental Association
Effective control of dental chair unit waterline biofilm and marked reduction of bacterial contamination of output water using two peroxide-based disinfectants
The Journal of Hospital Infection
Dental units: an environmental study of sources of potentially pathogenic mycobacteria
Tubercle and Lung Disease
A review of biofilms and their role in microbial contamination of dental unit water systems (DUWS)
International Biodeterioration and Biodegradation
Efficacy of anti-retraction devices in preventing bacterial contamination of dental unit water lines
Journal of Dentistry
Reduction of microbes in handpieces by flushing before use
Journal of the American Dental Association
Prevention of bacterial contamination of water in dental units
The Journal of Hospital Infection
Combining periodic and continuous sodium hypochlorite treatment to control biofilms in dental unit water systems
Journal of the American Dental Association
Use of chlorine dioxide to disinfect dental unit waterlines
The Journal of Hospital Infection
A simulated-use evaluation of a strategy for preventing biofilm formation in dental unit waterlines
Journal of the American Dental Association
In vitro modeling of dental water line contamination and decontamination
FEMS Microbiology Letters
Dental unit waterline antimicrobial agents’ effect on dentin bond strength
Journal of the American Dental Association
Effect of iodine on mercury concentrations in dental-unit wastewater
Dental Materials
Disinfectants’ effect on mercury release from amalgam
Journal of the American Dental Association
The effect of disinfectants and line cleaners on the release of mercury from amalgam
Journal of the American Dental Association
Inhibitory effect of PVDF tubes on biofilm formation in dental unit waterlines
Dental Materials
Microbiology and cross-infection control
The incidence and control of bacterial infection of dental units and ultrasonic scalers
British Dental Journal
Studies on dental aerobiology. IV. Bacterial contamination of water delivered by dental units
Journal of Dental Research
The significance of the bacterial contamination of dental unit water systems
British Dental Journal
Bacterial biofilm: a source of contamination in dental air–water syringes
Clinical Preventive Dentistry
Multiparametric analysis of waterline contamination in dental units
Applied and Environmental Microbiology
Disinfection of dental unit waterlines with an oral antiseptic
The Journal of Clinical Dentistry
Microbial biofilm formation and contamination of dental-unit water systems in general dental practice
Applied and Environmental Microbiology
Microbial biofilms: from ecology to molecular genetics
Microbiology and Molecular Biology Reviews
Biofilm, city of microbes
Journal of Bacteriology
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2018, Journal of Infection and Public HealthCitation Excerpt :This result is consistent with previous studies which demonstrated the microorganisms ranging from 102 to 108 CFU/ml [18–21]. Although some studies pointed out that tube diameters, water flow rates and service life of DCU may have influence on water quality in DUWLs [7,22–23], there was no significant difference among DCUs in terms of different departments, brands or service lives in the present studies. However, Barbeau et al. noted that just 4% or less microbial communities can be cultured from DUWLs [4].